This invention relates to a multiroom air conditioner of the type having a plurality of indoor air conditioning units connected to a single outdoor air conditioning unit.
FIG. 1 is a schematic diagram of a conventional single-room, separate-type air conditioner having a single indoor air conditioning unit (hereinunder referred to as an indoor unit) which is connected to a single outdoor air conditioning unit (hereinunder referred to as an outdoor unit). The indoor unit consists primarily of an indoor heat exchanger 5. The outdoor unit comprises a compressor 1, a four-way valve 2 which is connected to the discharge side of the compressor 1, an outdoor heat exchanger 3 which is connected to the four-way valve 2 and the indoor heat exchanger 5, an accumulator 4 which is connected between the four-way valve 2 and the suction port of the compressor 1, and a throttling mechanism in the form of two capillary tubes 7 which are connected in series between the outdoor heat exchanger 3 and the indoor heat exchanger 5. A check valve 8 is connected in across one of the capillary tubes 7. Switching between cooling operation and heating operation is performed by switching the four-way valve 2 from the position shown by the solid lines (cooling mode) to that shown by the dashed lines (heating mode). The solid arrows show the flow of refrigerant during cooling mode, and the dashed arrows illustrate the flow during heating mode. As throttling is performed by capillary tubes 7, the refrigerant circuit of a single-room separate-type air conditioner is extremely simple and inexpensive.
In contrast, a multiroom air conditioner having a single outdoor unit and a plurality of indoor units has a much more complicated structure. FIG. 2 is a schematic diagram of a conventional multiroom air conditioner which was disclosed in Japanese Utility Model Laid-Open No. 55-28993. Elements numbers 1 through 4 are the same as in FIG. 1, while elements 5a and 5b are a pair of indoor heat exchangers of two indoor units which are connected in parallel to the outdoor heat exchanger 3 of an outdoor unit. Two gas-side solenoid valves 6a and 6b are installed on the gas-side branch pipes for the two indoor heat exchangers 5a and 5b, and two liquid-side solenoid valves 10a and 10b are installed on the liquid-side branch pipes. In addition to a throttling mechanism for the outdoor unit in the form of an expansion valve 9 which is connected in parallel with a check valve 8 between the outdoor heat exchanger 3 and the liquid-side solenoid valves 10a and 10b, two expansion valves 11a and 11b are installed on the liquid sides of the two heat indoor exchangers 5a and 5b. Two check valves 12a and 12b are connected in parallel with the expansion valves 11a and 11b, respectively. A receiver 13 for liquid refrigerant is connected in series between the outdoor expansion valve 9 and the liquid-side solenoid valves 10a and 10b. As in FIG. 1, the solid arrows indicate refrigerant flow during cooling mode and the dashed arrows indicate flow during heating mode.
The indoor units of conventional single-room, separate-type air conditioners are manufactured in large quantities and are relatively inexpensive, so it is desirable to be able to employ them as the indoor units of multiroom air conditioners. However, it can be seen from comparison of FIG. 1 and FIG. 2 that as the indoor unit of a multiroom air conditioner must be equipped with expansion valves and check valves, it is difficult to adapt an indoor unit of a single-room air conditioner for use in a multiroom air conditioner.
In addition, in the conventional multiroom air conditioner of FIG. 2, since control of the degree of superheat is performed by expansion valves during cooling and heating mode, it is necessary to provide a receiver 13, and therefore two vessels for receiving refrigerant (the accumulator 4 and the receiver 13) are required to prevent refrigerant from flowing back into the compressor 1 during a transitory state.
Furthermore, in a conventional multiroom air conditioner, the liquid refrigerant at the confluence point of the liquid-side branch pipes is under high pressure during heating operation. lf even one of the indoor units is stopped, it is necessary to provide an unillustrated refrigerant recovery circuit comprising a check valve and a capillary tube for recovering the refrigerant within the halted unit and bringing it to the low-pressure side of the compressor. As a result, the overall refrigerant circuit ends up being complicated.